Many ceramic and metallic materials exhibit increased strength, and often toughness, when reinforced with a second phase in the form of fibers, whiskers or particulates. However, the processing required to uniformly disperse the reinforcing phase within the matrix material is often cumbersome and ineffective. For example, U.S. Pat. 5,080,977, issued Jan. 14, 1992, to Isidor Zaplatynsky describes two methods of forming composite powder materials. In the first method, ceramic and glass powders are mixed together and sintered at 1400.degree. C. for 10 to 15 hours. The sintered material is then crushed to obtain a composite powder having a particle size suitable for plasma spray deposition. In the second method, a sol-gel paste mixture comprising ceramic particles coated with gel (the precursor of a glass phase) is heated and dried to form an intermediate agglomerate The agglomerate is then heated to 1300.degree. C. and held at that temperature for several hours, after which the material is comminuted by crushing.
Such methods of forming coated particles are inherently time-consuming and costly and, if the respective powders are not uniformly dispersed prior to sintering, are prone to segregation defects. Furthermore, as a result of the required comminution after sintering, the size and shape of the particles is compromised For example, composite materials having fibers or other elongate reinforcement components, such as ceramic whiskers, cannot be formed by the above described methods because crushing would break the fibers.
The present invention is directed to overcoming the problems set forth above. It is desirable to have an economical method for coating the reinforcement component of composite materials with the matrix component so that segregation of the components is avoided during subsequent deposition or dry forming. It is also desirable to have such a method that is substantially nonreactive and does not damage or otherwise alter the structural shape of the reinforcement component.